Great! What’s the difference?
Adjectives modify (describe) nouns and pronouns; adverbs modify verbs, adjectives, and other adverbs.
What does that mean to me?
If you are thinking about hyphenating two words and the first one modifies the second, DON’T DO IT!
The nearly identical twins were causing a ruckus. (‘Nearly’ tells how identical.)
The partly cloudy skies suggested rain. (‘Partly’ tells how cloudy.)
2. Do hyphenate between adjectives that work together as one idea to modify a noun-but the adjectives must come before the noun!
He built a two-story barn. (It isn’t a two barn, and it isn’t a story barn-it’s a two-story barn!)
His barn has two stories. (The adjectives come after the noun, so don’t hyphenate.)
3. Do hyphenate phrases that act as one idea (and come before the noun).
This was a once-in-a-lifetime opportunity.
But not: This kind of opportunity only comes once in a lifetime.
4. To be continued: Dashes vs. Hyphens . . .